Add support for PNG representation in gfx::Image

tools/valgrind/memcheck/suppressions_mac.txt

Index: tools/valgrind/memcheck/suppressions_mac.txt
diff --git a/tools/valgrind/memcheck/suppressions_mac.txt b/tools/valgrind/memcheck/suppressions_mac.txt
index 826445b87b482bed6ada2fc59f794beeafb088ba..e3eba8f14178bc4ee146f84426fb0fa3c3a05778 100644
--- a/tools/valgrind/memcheck/suppressions_mac.txt
+++ b/tools/valgrind/memcheck/suppressions_mac.txt
@@ -316,6 +316,25 @@
    fun:_ZN5media18VideoCaptureDevice6CreateERKNS0_4NameE
    fun:_ZN5media45VideoCaptureDeviceTest_OpenInvalidDevice_Test8TestBodyEv
 }
+{
+  # See http://crbug.com/141293
+  bug_141293
+  Memcheck:Uninitialized
+  fun:deflateEnd
+  fun:deflateSetDictionary
+  fun:deflate
+  fun:png_write_finish_row
+  fun:png_write_find_filter
+  fun:_cg_png_write_row
+  fun:writeOnePng
+  fun:_CGImagePluginWritePNG
+  fun:CGImageDestinationFinalize
+  fun:+[NSBitmapImageRep(NSBitmapImageFileTypeExtensions) representationOfImageRepsInArray:usingType:properties:]
+  fun:-[NSBitmapImageRep(NSBitmapImageFileTypeExtensions) representationUsingType:properties:]
+  fun:_ZN3gfx8internal14PNGFromNSImageEP7NSImagePSt6vectorIhSaIhEE
+  fun:_ZNK3gfx5Image10ToImagePNGEv
+  fun:_ZN12_GLOBAL__N_143ImageTest_PlatformToPNGEncodeAndDecode_Test8TestBodyEv
+}
 
 # 2. Intentional unit test errors, stuff that is somehow a false positive
 # in our own code, or stuff that is so trivial it's not worth fixing.